Paperback books are commonly formed by the process of perfect binding wherein the individual sheets or leaves of a book are assembled and held together by a backbone adhesive, usually a hot melt glue, applied to the spine edges of the leaves to form a book block. The same adhesive which joins the sheets into a book block usually attaches the book block to the inner spine of a stiff paper cover. Paperback books may be produced according to this common method with efficiency and low cost; however, because the book block is affixed along the length of its back to the stiff paper cover the sheets of the book are not free to open fully and the pages in a spread will not lie flat. Books to be used as instruction manuals, cookbooks, workbooks, or textbooks should be readable without the need for the reader to place his hands on the book, so that he may carry on other tasks with his hands while reading the book. Furthermore, because of the stiffness of the spine of the book, when the book is opened a deep depression or "V" is formed at the binding. This deep "V" makes it difficult to read the printing at the inner margins of the bound pages.
A book binding is disclosed in U.S. Pat. No. 951,436 to Duryea which employs a tubular binding formed by adhesively overlapping an elongated piece or strip of pliant flexible material disclosed by Duryea as tough paper, muslin, or the like. However, a tube of ordinary flexible material such as paper or muslin may lack the strength and glue adhesion needed to durably bind the book back to the cover in a commercially acceptable manner. The disclosure of U.S. Pat. No. 998,283 to Duryea et al. recognizes this by providing additional strength to the binding of U.S. Pat. No. 951,436 by having lateral extending portions from the sides of the tubular book bindings which are glued between the back cover and the end sheets of a book. The tubular book bindings of the Duryea patents are not in widespread use. To be practical, a tubular binding requires a durable and flexible material exhibiting substantial tensile strength.
An attribute of most previous materials employed for tubular bindings is a tendency for the glue which is used to attach the tubular binding to the back of the -hook block and to the spine of the book cover to render the tubular material inflexible and brittle such that when the bound book is opened the glue in the area along the hinges between the cover and the book block cracks and breaks the material of the tube.
U.S. Pat. No. 4,547,000 to Sallinen teaches a method of overcoming the glue saturated enbrittlement of the tubular binding by wrapping the tubular binding around the side of the book back and leaving the portions so wrapped free of glue to form flexible hinges. Leaving these hinge areas unglued, however, involves additional cost and complexity in manufacturing. Sallinen discloses a tubular binding using some elastically flexible material such as plastic or crepe nonpenetrable by glue. The commercial embodiment of the Sallinen invention utilizes paper or paper reinforced with gauze mesh, both materials which must be kept glue free to remain flexible.
Another method for producing paperback bindings which allows the bound pages to lie flat is known which attaches the book block to a flexible crepe capping which provides support for the sheets of the book block but which is not directly attached to the spine of the cover, rather the book block is attached to the cover by stripes of glue affixing the first and last sheets of the book block to the stiff paper cover on either side of the cover's spine. Thus the entire weight of the book block is carried on only a small portion of a ribbon and two sheets of paper. Furthermore, this method requires that a portion of the first and last pages of the book block be given over to adhesive purposes.
What is needed is a paperback binding which would leave the book block free to bend--allowing the book to lie flat when opened--yet which is also sturdy and simple to manufacture.